Flame spray clad powder composed of a refractory material and nickel or cobalt



F J. DI

Y CLAD POWD ATERIAL A Filed fi l? Bow United States Patent 3 254 970FLAME SPRAY (:LADPowDER COMPOSED or A REFRACTORY MATERIAL AND NICKEL 0RCOBALT Ferdinand J. Dittrich, Bellmore, and Arthur P. Shepard, Flushing,N.Y., assignors to Metco, Inc., a corporation of New Jersey Filed Aug.16, 1961, Ser. No. 134,544 14 Claims. (Cl. 29-1835) This is acontinuation-impart of application Serial No. 72,543, filed November 22,1960, now abandoned.

This invention relates to the flame spraying of synergistic composites.The invention more particularly relates to the flame spraying ofsynergistically-clad flame spray powders, to a novel group of flamespray materials comprising such synergistically-clad flame spraypowders, and more broadly to the spraying of other synergisticcomposites wherein the synergistic action involves the generation ofheat.

Flame spraying involves the feeding of a heat-fusible material into aheating zone, wherein the same is melted or at least heat-softened andthen propelled from the heating zone in a finely divided form, generallyonto a surface to be coated.

The material being sprayed is generally fed into the heating zone in theform of either a powder or a wire (the latter term designating both rodsand wires). The spraying is effected in a device known as a heat-fusiblematerial spray gun or a flame spray gun.

In the wire type flame spray gun the rod or wire of the material to besprayed is fed into the heating zone formed by a flame of some type,where it is melted or at least heat-softened and atomized, usually byblast gas, and thence propelledin finely divided form onto the surfaceto be coated. The rod or wire may be a conventionally formed rod or wireof a metal, or may be formed by sintering together finely dividedmaterial or by bonding together finely divided material by means of aplastic binder or other suitable binder which disintegrates in the heatof the heating zone, thereby releasing the material to be spray-ed infinely divided form.

For spraying finely divided, i.e., powdered material, a powder typeflame spray gun is used in which the powder, usually entrained in acarrier gas, is fed into the heating zone of the gun formed by a flameof some type. The powder is either melted or at least the surface of thegrains heat-softened in this zone, and the thus thermally conditionedparticles propelled onto a surface to provide a coating. In the powdertype spray gun, as no atomizing energy is required, a separate blast gasis often dispensed with, though the same may be supplied in order to aidin accelerating the particles and propelling them toward the surface tobe coated.

The blast gas may be provided for both the wire type and powder guns toperform the additional function of cooling the workpiece and the coatingbeing formed thereon.

The heat for the heating zone is most commonly produced from a flamecaused by the combustion of a fuel, such as acetylene, propane, naturalgas or the like, using oxygen or air as the oxidizing agent. The heatmay, however, also be produced by an electrical arc flame or in thenewer type of guns, by a plasma flame. The plasma flame may in itselfconstitute part of an electric are or, in accordance with a newerdevelopment, may be in the form of a free plasma stream, i.e., a streamof plasma which may be considered independent of the are as it does notcontribute to the electric flow between electrodes.

Heat-fusible material spray guns utilizing electric resistance heatingor induction heating as the heat source have also been proposed but havenot proven commercially successful except in connection with thespraying of low melting point metals, such as solders, lead and zinc.

Flame spraying in the initial stages of its commercial development wasused mostly for the spraying of various metals and was often referred toas metallizing. However, the art of flame spraying extends to thespraying of a much wider group of materials, including higher meltingpoint or refractory metals, ceramic, cermets and the like, and suchmaterials are of increasing commercial interest.

In the case of spraying heat-fusible materials in the initial form of arod or wire, the rod or wire is generally of a single composition, i.e.,in the form of a specific metal, alloy, ceramic or the like. While it istrue that rods or wires formed from finely divided material boundtogether with a binder. of plastic or the like, as mentioned above, wereknown, the binder did not take part in the spraying or contribute to thecoating and merely served the purpose of maintaining the rod or wire inshape until fed into the heating zone.

In the case of flame spray powders, while powdersformed of severalconstituents were known, the same were generally in the form of a powdermixture of the individual constituents or, at best, a particleaggregate.

One object of this invention is the spraying of the heat-fusiblematerial in a novel form, which allows the I obtaining of superiorresults.

A further object of this invention is a novel group of flame sprayingmaterials.

These and still further objects will become apparent from the followingdescription read in conjunction with the drawings in which:

FIG. 1 diagrammatically shows a cross-section of a grain of a novelflame spray powder in accordance with the invention;

FIG. 2 is a diagrammatic cross-section of a further embodiment of agrain of a novel flame spray powder in accordance with the invention;

FIG. 3 is a diagrammatic cross-section of an embodiment of a novel flamespray rod or wire in accordance with the invent-ion; and

FIG. 4 shows an elevation of a further embodiment of a novel flame sprayrod or wire in accordance with the invention.

In accordance with a broad aspect of the invention the flame spraying iseffected with the material being sprayed in the form of a powder, theindividual grains of which are in the form of a clad compositeconsisting of nuclei and at least one coating layer of a differentmaterial which will synergistically act with the nuclei in the process.

Each grain of the synergistically clad composite powders may also be inthe form of a nucleus with two or more diiferent coating layers whichwill synergistically act with each other and/ or with the nucleus.

The synergistic action of the coating layer with the nucleus and thecoating layers with each other, as the case may be, may manifest itselfas a chemical or physical action or both, and may appear in the heatingzone and/ or along the path of travel to the surface to be coated, or atthe sprayed coating as sprayed, or after a subsequent treatment such asa heatingor fusing operation.

The synergistic action between the nuclei and/ or the coating layer orlayers may, for example, involve the physical or chemical generation ofheat by exothermic reaction in the heating zone, along the path oftravel to the target, or on the coated surface itself, so as to increasethe thermal efliciency of the process, aid in the bonding of the coatingand/or produce results and effects by this in situ generated heat whichcannot be achieved by the externally supplied heat. The synergismresulting in the exothermic reaction may be caused by the utilization oftwo components which will combine at the temperatures involved to form amaterial with a melting point higher than that of either of theconstituents, with a considerable release of heat, by the use ofcomponents which will chemically combine in exothermic reaction, as forexample where one acts as an oxidizing and the other a reducing agent,or by the use of components which will dissolve together in generationof heat or the like.

Thus, for example, one of the components may be a nickel-containingcomponent and the other an aluminumcontaining component which willcombine under the spraying conditions to form a nickel-aluminuminter-metallic compound with an exothermic reaction. Similarly, one ofthe components may contain the aluminum and the other antimony, calcium,cobalt, lanthanum, lithium, manganese, nickel, palladium, praseodymium,dysprosium, or a combination thereof which, upon combining during thespraying, form a higher melting point compound with the generation ofheat. Similarly, the clad-composite powder may be a combination ofnickel with elemental phosphorus, silver, copper, aluminum or the like,which will combine in exothermic reaction.

The synergistic action may also involve a protective effect of thecoating material on the nuclei or a lower coating layer in order toprevent loss or destruction of this under-material and allow thespraying of the combination. Thus, for example, nickel may be coated onnickel-phosphorus, nickel-boron, or the like in order to prevent loss ordestruction of the fiuxing agent and allow the formation of aself-fiuxing coating, as for example in the spray-weld process.

The synergism may also involve a bonding effect in order to allow asatisfactory bonding on a base of sprayed materials which normallypresent bonding difiiculties, as for example the synergism of a matrixmetal, such as nickel or cobalt, with a hard or refractory material,such as tungsten carbide, A1 diamonds or other hard gems or the like.

Bonding to the base or substrate being coated may also be aided by thesynergistic action of exothermic reaction, as for example in the case ofnickel-coated aluminum powder.

The synergistic effect may also involves the combining of the componentsto form a third component, such as a compound or alloy or inter-metalliccompound desired as the coating constituent. This may involve adissolving together of the components, alloying the components, or achemical reaction between components which may be endothermic in natureif sufficient heat is available for the process.

The powder particles may be in the form of a nucleus with a singlecoating layer, or may be in the form of a nucleus with a multiple numberof layers of the same or different materials.

The clad powders in accordance with the invention may be formed in anyknown or desired manner and preferably by the known chemical platingprocesses in which a coating material is deposited on a seed or nucleusof another material, or in which multiple layers of various materialsare built up on the seed material, or in which various materials areco-deposited in a single layer on the seed material.

A preferred mode of forming the clad powders involves the depositing ofa metal from a solution by reduction on a seed or nucleus, such as thehydrogen reduction of ammoniacal solutions of nickel and ammoniumsulphate on a seed powder catalyzed by the addition of anthraquinone. Itis also possible to form the coating by the use of other known coatingprocesses, such as coating by vapor deposition, by the thermaldecomposition of metal carbonyls, by hydrogen reduction of metal halidevapors, by thermal decomposition of halides, hydrides, carbonyls,organometals or other volatile compounds, or by displacement gas platingand the like.

The clad powders for this invention should have the general over-allshape and size of conventional, flamespray powders, and thus for exampleshould have a size between 60 mesh and +3 microns and preferably l40 and+10'microns (U.S. standard screen mesh size). Most preferably the powdershould be as uniform as possible in grain size, with the individualgrains not varying by more than 250 microns and preferably microns.

Depending on the particular flame spray process and the desired purpose,the clad powders may be sprayed per se or in combination with otherdifferent clad powders, or in combination with other conventional flamespray powders or powder components.

FIG. 1 diagrammatically shows an embodiment of a clad powder having anucleus of aluminum and a coating of nickel.

FIG. 2 shows a multi-layer powder of nickel and copper on nickel-boron.

While the powders are preferably sprayed, as such, in a powder-type offlame spray gun, it is also possible to combine the same in the form ofa wire or rod, using a plastic or similar binder which decomposes in theheating zone of the gun, or, in certain cases the powders may becompacted and/ or sintered together in the form of a rod or wire.

In the limited case where the synergistic action of the componentsinvolves an exothermic reaction as, for example, the combination ofnickel and aluminum to form the nickel-aluminum inter-metalliccompounds, the spray material may assume a form other than the cladpowder and may, for example, be in the form of a suitable aggregate or acomposite wire, such as a wire having a coating sheath of one material,such as nickel, with a core of the other material, such as aluminum, asshown in FIG. 3, or wire formed by twisting together and rollingseparate wires of components, such as nickel and aluminum, as shown inFIG. 4. Various combinations of other exothermically-reacting componentsmay of course be used in the formation of such Wire, which exothermicreaction will substantially contribute to the heat economy of the flamespraying and may even show self-ignition characteristics when fedthrough the spray gun.

The following examples are given by way of illustration and notlimitation:

EXAMPLE 1 An aluminum powder having a particle size between mesh and+325 mesh (U.S. standard screen size) is coated with nickel in the knownmanner by the hydrogen reduction of an ammoniacal solution of nickel andammonium sulphate, using anthraquinone as the coating catalyst. Thereduction is effected at a temperature between about 300 and 350 F. in amechanically agitated autoclave using solutions containing 40-50 gramsper liter of nickel and 10-400 grams per liter of (NH SO and 2030 gramsper liter of NH About .2 gram per liter of anthraquinone is used as thecatalyst and the autoclave is pressurized with hydrogen at a pressure ofabout 300 lbs. p.s.i.g. After the nickel solution is depleted and thealuminum coated with an initial coating of nickel, the solution isdischarged from the autoclave and replenished with a fresh solutionwhich need not contain further amounts of the anthraquinone coatingcatalyst, as the initially formed nickel coating in itself acts as acatalyst. The cycle is continuously repeated until a composite powder isformed containing about 16 to 18% by weight aluminum and 84 to 82% byweight of nickel, and a size of l00 to +270 mesh.

The powder thus formed is flame-sprayed on a mild steel plate which hasbeen surface-cleaned with emery cloth. The spraying is effected at about7 inches from the plate, using a powder-type flame-spray gun asdescribed in US. Patent 2,961,335, issuing November 22, 1960 and sold byMetco, Inc. of Westbury, Long Island, N.Y., under the trade name ofThermospray powder gun. The spraying is efiected at a rate of 6 to 9lbs. of powder per hour, using acetylene gas as the fuel at a pressureof 10 p.s.i. and a flow rate of 17 to 25 cu. ft./hr. and oxygen as theoxidizing gas at a pressure of 12 p.s.i. and a flow rate of 29 to 35 cu.ft./hr.

' The nickel coating and the aluminum base combine in the heat of theflame with a strong exothermic action, forming a nickel aluminuminter-metallic compound which deposits on the base as a dense, highquality coating which exhibits self-bonding characteristics. A coatinglayer of .002-.004 thickness is built up in this manner. The coating maybe used as a base material for spraying of further layers of differentmetals or the like and serves as an excellent intermediate bondinglayer.

vThe coating layer may also be built up to a greater thickness as, forexample, .004"-.008", for use as an oxygen barrier under-coat, or toeven greater thickness as, for example, .020"-.040" or thicker as awearresistant, oxidation-resistant surface.

Due to its self-bonding characteristics the sprayed coating will adhereto a base without the conventional surface preparation or roughening,and due to the natural characteristics of a sprayed material, will allowfurther materials to be sprayed thereon with good bonding. The coatingformed from the powder has excellent oxidationresistant characteristicseven at high temperatures and in oxidizing atmospheres, and will forexample eliminate the oxidation of base materials, such as molybdenum orthe like. The sprayed coatings may be used as a lining in metal-meltingcrucibles or molten metal-handling equipment, and will not be wetted orpenetrated by many molten metals, including self-fluxing alloys.Coatings formed of the sprayed material also show good potential as hightemperature, wear-resistant coatings.

When the example is repeated on a molybdenum rod of diameter, with acoating between .008.010 thick, the coated rod may be repeatedly heatedto approximately 2000 F. in air, with a welding torch, and cooled toroom temperature with no visible oxidation occurring.

Similar results may also be obtained if the composite powder contains-45% by weight of aluminum and 55-90% by weight of nickel.

EXAMPLE 2 Example 1 is repeated with the spraying being effected in turnon the following bases and prepared in the following manner:

Low alloy steels and stainless steels, smooth-ground to remove surfacecontamination; copper .and copper base alloys, rough-ground orlight-grit-blasted; aluminum and aluminum base alloys, rough-ground orlight-grit-blasted; magnesium, rough ground or light-grit-blasted; andtitanium, rough-ground or light-grit-blasted.

In each case when a further material, such as steel, alumina or thelike, was sprayed over the coating in the conventional and well knownmanner, the same was bonded with a tenacious bond, though if thismaterial had been initially sprayed on the surface as prepared in themanner indicated above, a satisfactory bond would not be obtained.

EXAMPLE 3 The nickel-clad powder of Example 1 is mixed with an A1 0powder having a particle size between 62 microns and 10 microns, in theratio of about 40% of the nickelclad powder with 60% by weight of theceramic. The powder is sprayed, using the gun described in Example 1,

. on a mild steel plate which has been surface-cleaned by It is possibleto vary the percentages of the ceramic in the mixture between 5 and'85%in order to vary the properties of the coating. With an increased amountof the inter-metallic compound in the cermet coating formed, the bondingand thermal shock-resistant properties increased, whereas with anincreased amount of the ceramic the hardness and wear-resistantproperties of the coating are increased and the thermal conductivitydecreased.

EXAMPLE 4 Example 3 is repeated, using the following materials in placeof the aluminum oxide:

Zirconia, calcium zinconalte, magnesium ziir'conate, spinel, cericoxide, hafnium oxide, mare earth oxides, molybidenum ldisilicide,tungsten silioide, chromium silicide, titanium silicide, tungstencarbide, titanium carbide and chromium carbide.

In each case an excellent coating was formed.

EXAMPLE 5 may be subsequently fused by a welding torch or furnace heatedto form a homogenous-pore-free coating welded to the base material.

EXAMPLE 6 A nickel-boron powder is coated with nickel to form acomposite flame-spray powder having a size between 120 and 325 mesh andcontaining 70 to nickel, based on the nickel boron. The powder wassprayed in the manner described in Example 1 and a high quality ofself-fluxing coating was formed.

The coating is mechanically bonded to the base and may be subsequentlyfused with a welding torch or in a furnace to form a dense homogenous,non-porous coating. When applied to a reactive base material, such asmolybdenum, in a thickness of .006" to .010" or heavier, the coating canbe fused to the base material by a torch or furnace without atmospherecontrol and below the recrystallization temperature of pure molybdenum,and .will protect the molybdenum base from an oxidizing atmosphere atelevated temperatures up to the melting point of the nickel-boroncoating.

EXAMPLE 7 Metallic cobalt is deposited as a coating on zirconia powderby the reduction of a cobalt ammonium sulphate solution with hydrogen soas to form a cobalt-clad zirconia flame-spray powder having a sizebetween 140 mesh and 15 microns and containing 25 to cobalt, based onthe zirconia. The material is sprayed in the manner described in Example1 on a grit-blasted base and a cermet coating is formed which showsexcellent adhesion to the base and which willretard oxidation of thebase. The coating furthermore has a high degree of hardness even atelevated temperatures, excellentshock-resistance andabrasion-resistance, and the metal matrix material is evenly distributedthroughout the applied coating.

It is possible to vary the percentages of the ceramic in the compositionbetween about 5 and 75% by weight in order to vary the properties of thecoating. With an increased amount of ceramic in the cermet coating, thehardness and wear-resistant properties of the coating arecorrespondingly increased and the thermal conductivity decreased.Conversely, with an increasing amount of the cobalt matrix the bondingand shock-resistant properties are increased.

7 EXAMPLE 8 A1 powder of a mesh size betweenSOrnicrons and 10 microns'is' coated with nickel in the manner I I described :in Example 1 toproduce a composite powder 7 containing 25 to 95% of the nickel based onthe alu mesh andilS microns. The powderis sprayed in the mannerdescribed in Example 1 on a gritblasted b ase,

and a cermet' coating is formed which shows excellent minurn oxide andhaving a particle size between 140 I I adhesion to the base, a highdegree of hardness e ven at elevated temperatures, and excellent thermalshock and abrasion-resistant characteristics.

I is evenly distributed throughout the sprayed coating.

In thiscase too it is possible to varythe percentage of the ceramic inthe composite between and 75 by weight, and withan increasing amount ofceramic, the,

hardness and wear-resistant properties increase, whereas I with anincrease of, the nickel, the thermal conductivity,

' bonding and: 'shockresistant properties are increased.

- EXAMPLE 9 I I Industrial diamond powder having a size between I 120and +140 mesh was coated with nickel in the manner described in Example1 so that the nickel-clad composite powder formed contained. about 25to- 50% an excellent bone or lap in which the diamonds were'firmlybonded in place.

w EXAMPLE-IO@,

Cobalt-bonded tungsten carbide particles of sharp, an- I 'gular shape:were coated with I nickel in the I manner de scribed in Example 1 so. asto produce a nickel-clad I flame'spray powder having a particlesizebetween. 100 I and 325 mesh and containing 20 to 50% nickel based onI I the tungsten carbidcr The powder was sprayed in the manner describedin Example 9, with the formation of I an excellent cutting hone or lap.The sharp angular I edges of the initial tungsten carbide were retainedin the coating.

Similar results were obtained when using crystalline tungsten carbide inplace of the cobalt bonded tungsten carbide particles.

EXAMPLE 11 EXAMPLE 12 A nickel boron powder is coated with copper andthe copper-coated composite further coated with nickel to form acomposite-clad flame spray powder having a particle size between 100 and325 mesh containing 63 to 67% nickel and 26 to 32% copper and 2 to boronby weight. The powder is sprayed in a powdertype flame spray gun on alightly grit-blasted steel base with the flame spray gun and method asdescribed in Example 1. An excellent self-fluxing alloy is formed, whichwhen fused in place by heating with an acetylene torch, forms a densecoating which corresponds in characteristics to Monel.

The metal matrix 8 EXAMPLE 13 A nickel boron powder is coated withchromium and t the resulting coated powderinturn coated with nickel soas to form a, flame spray composite-clad powder having, amesh, sizebetween 100 and 3,25 and containing 170 t Wm 80% nickel and 18 to 20%:chrome I and :2 to 1'0%' I I boron by weight, Thepowder is sprayedin themanner described in Example 12, resulting in ,a self-fluxing alloycoating which,when fused inplace in the manner described: in Example 12,produces a high grade coating having characteristics similar to NichromeV,

EXAMPLE 14 Nickel-bonded titanium carbide particles having a sizebetween 140 and .325 meshare coated with nickel, as I =Jdescribed inExample 1, so as to produce a nickel-clad :fiame spray powder havinga'particle size between 1:00 and p 270 mesh and/containing 20 to nickelbased on I Ithe titaniumcarbide. The material is'sprayediin the/ mannerdescribed in Example 1 on a base with surface roughened bygrit-blasting, and a high grade, bonded titanium carbide coating isformed in which the nickel acts as a r'natrix'binding' material.

' I i When properly: finished by grinding, the'resultant coat-I ing isan excellent hard-facing, extremely resistant-to; -wear coating even'atelevated temperatures. I I I Similar results are obtained when usingcrystalline titanium carbide particles in 'place' of the nickelsbonded:I titanium carbide particles, I I I I EXAMPLE 15 Copper powder, iscoated with nickel, in the manner, I described in Example 1 so as toform a nickel-clad,

composite flame spray powder having a particle size be- I I tween IOOand325 mesh and containing to nickel based on the. copper. Upon sprayingin, the manner described in Example 1011 a base roughened by Igrit-blasting or other'means, an excellent, corrosion and1oxidation-resistantcoating is formed. A similar coating 'is formed itthe copper is replaoed withchr-omium in an amount of 15 to-25% chromiumbased on the nickel.

EXAMPLE 16 Molybdenum disilicide powder is coated with nickel in themanner described in Example 1 so as to form a composite-clad flame spraypowder having a particle size between 140 mesh and 10 microns, andcontaining 15 to 40% nickel by weight based on the disilicide. Thepowder is sprayed with the flame spray gun described in Example 1 on abase material roughened by grit-blasting.

The resultant oxidation-resistant coating is very dense, but may befurther improved by subsequent heat treatment in a neutral to reducingatmosphere.

EXAMPLE 17 Example 10 is repeated except in place of the nickel, nickelphosphorus is used containing 4 to 12% of phosphorus. A similar coatingresulted upon spraying, which however was self-fiuxing.

EXAMPLE 18 EXAMPLE 19 Silver solder powder is coated with nickel in themanner described in Example 1 so as to produce a nickelclad compositepowder having a size between and 325 mesh and containing 25 to 50%nickel based on the Upon spraying in the manner described silver solder.

resistant coating.

in Example 1 on a base material prepared by grit-blasting, a low-fusingtemperature, sel-f-fluxing coating is formed which, when subsequentlyfused, is a homogenous, porefree coating securely fused to the basematerial.

A simple mixture of powders consisting of 20 to 65% of thisnickel-coated silver solder and 35 to 85% of a carbide (Example 10) issprayed in the manner described in Example 1. The resultant coating,when fused, consists of angular carbide particles securely bonded toeach other and to the base material.

The fused coating may be suitably finished by grinding for use as awear-resisting coating or used, as .fused, where the coated article isto be used as a hone or lap, the sharp edges of the carbide inclusionsconstituting the abrading or cutting edges. I EXAMPLE 20 Titanium iscoated with nickel as described in Example 1 to produce a powder havinga particle size between 100 and 325 mesh and containing 10 to 50% nickelbased on the titanium.

The nickel protects the titanium from oxidation during storage and whenspraying.

Upon spraying in the manner described in Example 1, on a base materialprepared by grit-blasting, the nickel and titanium combine in the flameto form a corrosion- EXAMPLE 21 A niobium powder is coated with nickelin the manner described in Example 1 so as to form a compositenickelclad flame spray powder having a particle size between 100 and 325mesh and containing to 40% by weight of nickel based on the niobium.

The nickel protects the niobium from oxidation during storage and whenspraying.

Upon spraying in the manner described in Example 1 on a base materialprepared by grit-blasting, the nickel and niobium combine in the flameto form a corrosionresistant material.

EXAMPLE 22 A molybdenum powder was coated with nickel in the mannerdescribed in Example 1 so as toproduce a nickelclad flame spray powderhaving a particle size between 100 and 325 mesh and containing 5 .to 40%nickel based on the molybdenum.

The nickel protects the molybdenum from oxidation during storage andwhen spraying.

Upon spraying in the manner described in Example 1 on a base-materialprepared by grit-blasting, the nickel and molybdenum combine in theflame to form a corrosion-resistant material.

EXAMPLE 23 A titanium boride powder was coated with nickel so as to forma flame spray powder having a particle size between 100 and 325 mesh andcontaining 20 to 50% nickel based on the titanium bor-ide.

The nickel protects the titanium boride during the spray.

Upon spraying in the manner described in Example ,1, on a base materialprepared by grit-blasting, a securely bonded nickel-titanium bor-idecomposite coating is achieved.

EXAMPLE 24 A silver powder is coated with nickel so as to form anickel-clad flame spray powder having a particle size between 100 and325 mesh and containing 30 to 70% nickel based on the silver.

Upon spraying in the manner described in Example 1, on .a base materialprepared by grit-blasting, the nickel and silver combine in the flame toproduce a new material which is securely bonded to the base and isexcellent for use as electrical contacts or the like.

During the spraying heat was evolved upon the combination of the nickeland silver, increasing the thermal economy of the process.

EXAMPLE 25 An aluminum powder is copper-plated so as to form acopper-clad flame spray powder having a particle size be tween 100- and325 mesh and containing to 98% or 8 to 20% copper based on the aluminum.

Upon spraying in the manner described in Example .1, on a base materialprepared by grit-blasting, the copper and aluminum combined in the flameto form a harder, corrosion resistant alloy.

EXAMPLE 26 A silicon powder was coated with copper so as to form acopper-clad flame spray powder having a particle size between 100 and325 mesh and containing 50 to 80% by weight of copper based on thesilicon.

Upon spraying in the manner described in Example 1, on a base materialprepared by grit blasting, the copper and silicon combine in the flameto form coatings of a material considerably more inert than copper.

EXAMPLE 27 EXAMPLE 28 Tin powder is coated with copper so as to form acopper-clad composite flame spray powder having a mesh size between 100and 325 mesh and containing 75 to copper-based on the tin.

Upon spraying in the manner described in Example 1, upon a base materialprepared by grit-blasting, the copper and tin combined in the flame toproduce a ductile, corrosion-resistant coating.

EXAMPLE 29 Lead powder is coated with copper so as to form compositeflame spray powder having a particle size between and 325 mesh andcontaining 50 to 90% copper based on the lead.

Upon spraying in the manner described in Example 1, upon a base materialprepared by grit-blasting, an excel lent, leaded copper material isdeposited which is suitable for use as a bearing.

EXAMPLE 30 The nickel-clad flame spray powder of Example 1 is mixed withabout 20% by weight of low pressure polyethylene powder and molded at atemperature of about 212 F. into the form of a rod of /s" diameter. Therod is sprayed, using a conventional wire-type flame spray gun sold byMetco, Inc. of Westbury, Long Island, N.Y., as the Metco-type 4E Gun.The spraying is effected with acetylene at a pressure of 15 p.s.i. and aflow rate of 37 cu. ft./hr. with oxygen as oxidizing gas at a pressureof 38 p.s.i. and a flow rate of 75 cu. ft./hr.; with air as a blast gasat a pressure of 40 p.s.i. and a flow rate of 25 cu. ft./min. The endcoating produced is similar to the coating produced in Example 1.

EXAMPLE 31 at a pressure of 15 p.s.i. and a flow rate of 37 cu. ft./hr.with oxygen as the oxidizing gas at a pressure of 38 p.s.i. and a flowrate of 75 cu. ft./hr. Air is used as a blast gas at a pressure of 55p.s.i. and a flow rate of 30 cu. ft./min. The end coating produced issimilar to the coating produced in Example 10.

EXAMPLE 32 A wire is formed by encasing a core of aluminum in a tube ofnickel and drawing to a size of .125 in diameter plus or minus .002. Thewire contains 82 to 84% by weight of nickel based on the aluminum.

The wire is sprayed, using a conventional wire type flame spray gun soldby Metco, Inc. of Westbury, Long Island, N.Y., as the Metco-type 4E Gun.Spraying is effected with acetylene at a pressure of 15 p.s.i. and aflow rate of 37 cu. ft./hr. with oxygen as the oxidizing gas at apressure of 38 p.s.i. and a flow rate of 75 cu.t ft./hr. Air is used asa blast gas at a pressure of 55 p.s.i. and a flow rate of 30 cu. ft./min. After initiation of the exothermic combination reaction at themelting wire tip, the flow of fuel and oxidizing gas may be drasticallyreduced, thus utilizing the heat of reaction to aid in melting the spraymaterial and contributing to the over-all economy of the process. Theend coating produced is similar to the coating produced in Example 1.

Similar results are also obtained using 55-90% by weight of nickel inthe wire.

EXAMPLE 33 A composite wire is formed by winding individual wires ofnickel and aluminum and drawing the same to a thickness of .125" plus orminus .002". The wire contains 82 to 84% by weight of nickel based onthe aluminum. The wire is sprayed in the manner described in Example 32,with identical conditions and coating resulting.

EXAMPLE 34 A self-fluxing silver-solder powder containing 15% silver, 5%phosphorus and 80% copper, is coated with copper so as to form acomposite flame spray powder having a particle size between 100 and 325mesh and containing to 50% copper based on the silver-solder.

Upon spraying in the manner described in Example 1, on a base materialprepared by light grit-blasting, an excellent, low melting point,self-fluxing alloy is deposited.

EXAMPLE 35 Example 34 is repeated except nickel is used in place of thecopper. Similar results are obtained.

EXAMPLE 36 A simple mixture of powders containing 10 to of the compositenickel-nickel phosphorus powder described in Example 5 and 75 to 90% ofcopper or copper alloy powder of the kind known as Everdur is sprayedwith the gun and spray conditions described in Example 1.

The coating as described is mechanically bonded to the base material andslightly porous by nature. It may be subsequently fused by torch orfurnace heating to form a homogenous, pore-free coating welded to thebase material. After fusion the coating is a fairly hard,corrosionresistant, welded bronze overlay.

EXAMPLE 37 Example 36 is repeated, using, however, the compositenickel-phosphorus powder described in Example 11 in place of thenickelnickel phosphorus powder.

Comparable results are obtained.

EXAMPLE 38 A simple mixture of powders containing 69% of the compositepowder as described in Example 6 and 31% pure copper powder in theparticle size range 140 and +325 mesh is sprayed with the gun asdescribed in Example 1.

The coating as applied may be subsequently fused without atmospherecontrol, to form a homogenous alloy fused to the base material, whichcorresponds in characteristics to Monel.

EXAMPLE 39 A simple mixture of powders containing 81% of the compositepowder as described in Example 6 and 19% of pure chromium powder in theparticle size range -140 and +325 mesh is sprayed with the gun asdescribed in Example 1.

The coating as applied may be subsequently fused without atmospherecontrol, to form a homogenous alloy fused to the base material, whichcorresponds in characteristics to Nichrome V.

EXAMPLE 40 Example 9 is repeated except in place of the nickel, nickelphosphorus was used containing 6 to 12% of phosphorus. A similar coatingresulted upon spraying, which however, was self-fiuxing. Fusion bondingof particles to each other and to the base was accomplished by fusingthe applied coating.

EXAMPLE 41 The coated diamond powder of Example 9 is mixed withnickel-coated silver solder powder of Example 19 in the proportion of 50to 75% diamond to 25 to 50% materix material.

The mixture was sprayed in the manner described in Example 1 and thedeposit subsequently fused.

The resultant coating was a dense, pore-free coating fused to the basematerial in which the diamonds were securely anchored by the low meltingpoint, self-fluxing matrix metal.

EXAMPLE 42 Example 14 is repeated except in place of the nickel, nickelphosphorus is used containing 4 to 12% of phosphorus. A similar coatingresulted which, however, was self-fluxing.

EXAMPLE 43 A silicon powder having a particle size between 140 and 325mesh is coated with molybdenum in the known manner and a compositepowder is formed containing about 35 to 39% by weight of silicon andabout 61 to 65%;1 by weight of molybdenum, and a size of to 270 mes Thepowder thus formed is flame-sprayed on a base material which has beenprepared by light grit-blasting, in the manner described in Example 1.

The molybdenum coating and the silicon base combine in the heat of theflame, forming a molybdenum silicon inter-metallic which deposits on thebase as a dense, high quality coating which exhibits excellentresistance to oxidation at elevated temperatures and will protect thebase material from oxidation.

EXAMPLE 44 A molybdenum powder having a particle size range between 140and 325 mesh is coated with silicon in the known manner and a compositepowder is formed containing about 35 to 39% by weight of silicon andabout 61 to 65% by weight of molybdenum, and a size of 100 to 270 mesh.

The powder thus formed is flame-sprayed on a base material which hasbeen prepared by light grit-blasting. The spraying is elfected at aboutfive inches from the plate, using a powder type plasma flame-spray gunsold by Metco, Inc. of Westbury, Long Island, N.Y., under the trade nameof Type MB Plasma Flame Gun. The spraying is efiected at a rate of sixto nine lbs. of powder per hour, using argon gas as the plasma gas at apressure of 100 p.s.i. and a flow rate of cu. ft./hr., using argon asthe powder carrier gas at 100 p.s.i. and a flow rate of 11.5 cu.ft./hr., using a No. 3 (pointed) electrode and rial from oxidation.

. 13 No. 3R argon nozzle, and using arc current of 550 amperes at 45volts.

The molybdenum base and silicon coating combine in the heat of theflame, forming a molybdenum silicon inter-metallic which deposits on thebase as a dense, high quality coating which exhibits excellentresistance to oxidation at high temperatures and willprotect the basematerial from oxidation.

EXAMPLE 45 p A silicon powder having a particle size between 140 and 325mesh is coated with chromium in the known manner, and a composite powderis formed containing about 48 to 85% chromium and 15 to 52% silicon byWeight and a size of 100 to 270 mesh.

The powder thus formed is flame-sprayed on a base material which hasbeen prepared by light grit-blasting in the manner described in Example1.

The chromium coating and the silicon base combine in the heat of theflame, forming a chromium-silicon intermetallic which deposits on thebase as a dense, high quality coating which exhibits excellentresistance to oxidation at elevated temperatures and will protect thebase material from oxidation.

EXAMPLE 46 A chromium powder having a particle size between 140 and 325mesh is coated with silicon in the known manner, and a composite powderis formed containing about 48 to 85% chromium and 15 to 52% silicon byweight and a size of 100 to 270 mesh.

The powder thus formed is flame-sprayed on a base material which hasbeen prepared by light grit-blasting. The spraying is effected at aboutfive inches from the plate, using a powder type plasma flame-spray gunsold by Metco, Inc. of Westbury, Long Island, N.Y., under the trade nameof Type MB Plasma Flame Gun. The spraying is eflected at a rate of sixto nine lbs. of powder per hour, using argon gas as the plasma gas at apressure of 100 p.s.i. and a flow rate of 110 cu. ft./hr., using argonas the powder carrier gas at 100 psi. and a flow rate of 11.5 cu.ft./hr., using a No. 3 (pointed) electrode and No. 3R argon nozzle, andusing arc current of 550 amperes at 45 volts. A p I The chromium baseand silicon coating combine in the heat of the flame, forming a chromiumsilicon intermetallic which deposits on the base as a dense, highquality coating which exhibits excellent resistance to oxidation at hightemperatures and will protect the base mate- EXAMPLE 47 A zirconiumpowder having a particle size between 140 and 325v mesh is coated withchromium in the known manner and a composite powder is formed containingabout 47%, zirconium and 53% chromium by weight and a size of 100 to 270mesh.

The powder thus formed is flame-sprayed on a base material in the mannerdescribed in Example 1.

The chromium coating and the zirconium base combine in the heat of theflame, forming a chromium zirconium inter-metallic which deposits on thebase as a dense, high quality coating which exhibits excellentresistance to oxidation at high temperatures.

EXAMPLE 48 A titanium powder having a particle size range betwen 140 and325 mesh is coated with chromium in the known manner and a compositepowder is formed containing about 35% chromium and 65% titanium byweight and a size of 100 to 270 mesh.

' The powder thus formed is flame-sprayed on a base material which hasbeen prepared by light grit-blasting in the manner described in Example1.

The chromium coating and the titanium base combine in the heat of theflame, forming a chromium titanium inter-metallic which deposits on thebase as a dense, high quality coating which exhibits excellentresistance to oxidation at high temperatures.

EXAMPLE 49 A titanium powder having a particle size range between 140and 325 mesh is coated with silicon in the known manner and a compositepowder is formed containing about 35 to 65% titanium and 35 to 65silicon by weight and a size of to 270 mesh.

The powder thus formed is flame-sprayed on a base material which hasbeen prepared by light grit-blasting. The spraying is effected at aboutfive inches from the plate, using a powder type plasma flame-spray gunsold by Metco, Inc. of Westbury, Long Island, N.Y., under the trade nameof Type MB Plasma Flame Gun. The spraying is effected at a rate of sixto nine lbs. of powder per hour, using argon gas as the plasma gas at apressure of 100 p.s.i. and a flow rate of cu. ft./hr., using argon asthe powder carrier gas at 100 p.s.i. and a fiow rate of 11.5 cu.ft./hr., using a No. 3 (pointed) electrode and No. 3R argon nozzle, andusing arc current of 550 amperes at 45 volts.

The titanium base and silicon coating combine in the heat of the flame,forming a titanium silicon inter-metallic which deposits on the base asa dense, high quality coating which exhibits excellent resistance tooxidation at high temperatures and will protect the base material fromoxidation.

EXAMPLE 50 A dysprosium powder having a particle size between and 325mesh is coated with aluminum in the known manner and a composite powderis formed containing 60 to 75% dysprosium and 25 to 40% aluminum byweight and a size of 100 to 270 mesh.

The powder thus formed is flame-sprayed on a base material which hasbeen prepared' by light grit-blasting in the manner described inExample 1. v

The aluminum'coating and the dysprosium base combine in the heat of theflame with a strong exothermic action, forming a dysprosium aluminuminter-metallic compound which deposits on the base as a dense, high.quality coating which exhibits excellent properties at hightemperatures.

EXAMPLE 51 A lanthanum powder having a particle size between 140 and 325mesh is coated with aluminum in the A chromium powder having a particlesize between 140 and 325 mesh is coated with aluminum in the known'manner and a composite powder is formed consisting of 60 to 62% chromiumand 38 to 40% aluminum by weight and a size of 100 to 270 mesh.

The powder thus formed is flame-sprayed on a base material which hasbeen prepared by grit-blasting in the manner described in Example 1.

The aluminum coating and the chromium base combine in the heat of theflame with a strong exothermic 15 action, forming a chromium aluminuminter-metallic compound which deposits on the base as a dense, highquality coating of very high melting point and excellentoxidation-resistance.

EXAMPLE 3 Example 52 is repeated except that the composite powder isformed with an aluminum core and chromium coating. Identical results areobtained.

EXAMPLE 54 The nickel-clad aluminum composite powder of Example 1 ismixed with cobalt bonded tungsten carbide particle powder having aparticle size range of l40 mesh microns, and preferably 140 +325 mesh inproportions of:

(a) 80 weight percent tungsten carbide to weight percent of thecomposite,

(b) 20 weight percent of the carbide to 80 weight percent of thecomposite, and

(c) preferably 50 weight percent each of the tungsten carbide andcomposite.

The powder mixtures are each flame-sprayed on a mild steel plate whichhas been surface cleaned by grinding or very light sand-blast cleaning.The spraying is effected at about 8-9 inches from the plate, using apowder-type flame-spray gun as described in US. Patent 2,961,335,issuing November 22, 1960, and sold by Metco, Inc. of Westbury, LongIsland, N.Y., under the trade name of Thermo-Spray powder gun. Thespraying is effected at a rate of 6 to 10 lbs. per hour using acetylenegas as the fuel at a pressure of 12 p.s.i. and a flow rate of 20 tocubic feet per hour and oxygen as the oxidizing gas at a pressure of 14p.s.i. and a flow rate of 30 to cubic feet per hour.

The nickel-aluminum composite powder in the mixture reactsexothermically in the flame to provide the selfbonding properties of themixture and, being fully molten on impact with the subtrate, becomes thematrix which securely binds the tungsten carbide particles together inthe coating.

Used as sprayed, or finished by proper grinding procedure, the resultantcoating is of a highly wear-resistant coating material, applicable tovirtually any base material and not subject to the limitations of thepreviously used self-fluxing alloy matrix materials which must be fusedat approximately 1900 F.

EXAMPLE Example 54 is repeated except that in place of the grade oftungsten carbide cobalt powder grains used, cobalt-bonded tungstencarbide grains with lower cobalt content and sharp, angular shape areused.

The powder was sprayed in the manner described in Example 54. The sharp,angular edges of the initial tungsten carbide particles were retained inthe coating.

The deposited coating may be suitably finished by grinding for use as awear-resisting coating or used as deposited where the coated article isto be used as a hone or lap, the sharp edges of the carbide inclusionsconstituting the abrading or cutting edges.

EXAMPLE 5 6 Example 55 is repeated except that in place of thecobalt-bonded tungsten carbide grains described, the nickel-cladtungsten carbide grains described in Example 10 were substituted.

EXAMPLE 57 The nickel-clad aluminum composite described in Example 1 ismixed with a columbium (niobium) powder of size between l20 mesh and +10microns and preferably 140 +325 mesh in the proportions of 60 Weightpercent of the nickel-aluminum composite.

The powder mixture is sprayed in the manner described in Example 54. Theresultant coating is self-bonding to a wide variety of substratematerials and when properly finished, by grinding or other means is ahighly wearresistant, hard coating.

EXAMPLE 58 The nickel-clad aluminum composite described in Ex ample 1 ismixed with a molybdenum powder of a size between 120 mesh and +10microns and preferably -140 +325 mesh in the proportions of 65 weightpercent molybdenum to 35 weight percent of the nickel-aluminumcomposite.

The powder mixture is sprayed in the manner described in Example 54. Theresultant coating is selfbonding to a wide variety of substratematerials and when properly finished by grinding or other means presentsa highly wear-resistant, hard surface.

EXAMPLE 59 Example 54 is repeated except in place of the tungstencarbide, other carbides such as titanium carbide, tantalum carbide,columbium carbide, chromium carbide and mixtures of the various carbidesare used.

EXAMPLE 60 The nickel-clad aluminum core composite from Example 54 ismixed with aluminum powder in the mesh size range +100 +325 mesh, andpreferably in the 170 +325 mesh size range in the proportions of weightpercent nickel aluminum composite to 20 weight percent aluminum.

The mixture was sprayed in the manner described in Example 54. Thecoating as deposited consists of an intimate mixture of theflame-reacted nickel aluminide and aluminum securely bonded to the baseand particle to particle within the coating.

Upon heat treating in the temperature range 1250 F. to 1500 F. inreducing atmosphere, dry hydrogen for instance, the nickel aluminide andaluminum combine to form a dense, homogenous coating fused to the basematerial which can be used for cathodic protection of iron and steelsubject to water and salt water corrosion.

EXAMPLE 61 The nickel-clad aluminum composite powder of Example 54 ismixed with Monel powder of a size between mesh and +10 microns, andpreferably between and +325 mesh in the proportions 35 weight percentcomposite to 65 weight percent Monel.

The powder mixture was sprayed in the manner described in Example 54.The resultant coating is selfbonding to a wide variety of substratematerials and the inclusion of the nickel-aluminum composite, thecomponents of which combine exothermically in the flame to provide theself-bonding ability of the mixture, considerably increase the particleto particle bonds within the coating and decrease the permeability ofthe coating.

EXAMPLE 62 Example 61 is repeated except that nickel and stainless steelpowders are substituted for the Monel.

EXAMPLE 63 Example 61 is repeated except that chromium is substitutedfor the Monel. The resultant coating when properly finished by grindingor other means shows high resistance to abrasion, wear, and galling byother metals, and is an excellent bearing surface. As may be noted fromthe foregoing the flame spraymg of synergistically-acting composites inaccordance with the invention is effected in the conventional manner,using the conventional flame spray equipment and utilizing conventionalsurface-preparation, though in certain instances wherein the spraycoating has self-bonding characteristics,

special surface-preparation other than a good cleaning, is not critical.

The synergistic composites in accordance with the invention may besprayed in conjunction with or in addition to other flame-spraymaterials conventionally used in the art, or may be sprayed incombination with or in conjunction with each other. Thus thesynergistically clad powders in accordance with the invention may besprayed in admixture with other conventional spray powders or mixturesof two or more of the composite powders in accordance with the inventionmay be sprayed.

In case of powders comprised of synergistically clad particles thecomponents of which exothermically react forming an inter-metalliccompound, the spraying in admixture with other composites or with otherconventional spray materials offers many advantages.

The use of these composite powders, such as nickelcoated aluminumparticles, will generally improve the bond of the total sprayed mixtureand thus of the other component or components to the substrate makingthe mixture self-bonding. The particle bond will also be improved sothat the porosity of the coating may be decreased. The use of thecomposites in admixture with conventional spray powders may thus be usedto improve the characteristics and properties of the materials or,conversely, the properties of the composites, such as the nickelaluminumdeposits may be enhanced or other new or better properties may beobtained.

In general as little as 20% by weight of the composite containingexothermically reacting components will be suflicient to substantiallyimprove the bonding characteristics and decreases the porosity of otherflamespray powders such as conventional metal or alloy powders. Thereis, of course, no upper limit on the amount as the composites may besprayed per se, but generally about 20% by weight of the other componentis required in order to have a pronounced effect on the characteristicsof the coating. When, for example, using a mixture of a nickel cladaluminum powder as for instance, is shown in Example 1, with tungstencarbide, titanium carbide, tantalum carbide, chromium carbide,molybdenum, niobium and tantalum amounts of 20% to 80%, and preferably25% to 50% by weight of the composite may be used. The mixtures areself-bonding as sprayed and form abrasion and wear-resistant coatings.When the same composite is sprayed in mixture with Monel, stainlesssteel, nickel, chormium, etc., amounts of 25 to 75% by weight of thecomposite, and preferably 30% to 40% by weight of the composite areused. When sprayed in admixture with aluminum as little as of thealuminum will vary the characteristics of the coating, though preferablyup to 25% of the aluminum is used. The composite as mentioned may alsobe sprayed in admixture with iron, nickel, or Nichrome or produce aself-bonding mixture which produces a coating of lower permeability. Itis of course, impractical to list all of the materials which may besprayed in conjunction or admixture with the composites in accordancewith the invention, but the selection of such materials for specificpurposes is within the skill of the artisan in light of the disclosure.

While the invention has been described in detail with reference tocertain specific embodiments, various changes and modifications whichfall within the spirit of the invention and scope of the appended claimswill become apparent to the skilled artisan. The invention is thereforeonly intended to be limited by the appended claims or their equivalentswherein we have endeavored to claim all inherent novelty.

We claim:

1. A flame spray powder in the form of individual, synergistically cladparticles of a size between about 60 mesh and plus 3 microns comprisinga nucleus and at least one coating layer of a material differing fromsaid nucleus, one of said coating layer and nucleus comprising arefractory selected from the group consisting of refractory oxides,refractory carbides, and diamond, the other a bonding matrix for saidrefractory material selected from the group consisting of nickel andcobalt matrices.

2. A flame spray powder according to claim 1 in which said nucleuscomprises a refractory material and said coating comprises a bondingmatrix for the material of said nucleus.

3. A flame spray powder according to claim 1 in which said coating layeris nickel and said nucleus is a refractory material.

4. A flame spray powder according which said coating layer is nickel anda carbide.

5. A flame spray powder according which said carbide is tungstencarbide.

6. A flame spray powder according which said coating layer is nickel andaluminum oxide.

7. A flame sp-ray powder according which said coating layer is nickeland diamond.

8. A flame spray powder according to claim 1 in which said powder isbonded in the form of a wire.

9. A flame spray powder according to claim 1 including at least oneadditional coating layer differing from said nucleus and first mentionedcoating layer and synergistically active with at least one of saidnucleus and first mentioned coating layer in flame spraying.

10. Flame spray powder according to claim 1 in which said refractorymaterial is a refractory oxide.

11. Flame spray powder according to claim 10 in which said refractoryoxide is a member selected from the group consisting of alumina andzirconia.

12.. Flame spray powder according to claim 1 in which said refractorymaterial is a refractory carbide.

13. Flame spray powder according to claim 12 in which said refractorycarbide is tungsten carbide.

14. Flame spray powder according to claim 1 in which said refractorymaterial is diamond.

to claim 1 in said nucleus is to claim 4 in to claim 1 in said nucleusis to claim 1 in said nucleus is References Cited by the Examiner UNITEDSTATES PATENTS 1,986,197 1/1935 Harshaw 0.55 2,288,869 7/1942 Wasserman11746 2,359,401 10/1944 Wulif 750.55 2,612,581 9/1952 Robinson 29--19'12,714,563 8/1955 Poorman et a1. 29194 2,904,449 9/1959 Bradstreet117105.2 2,908,589 10/1959 Gutzeit 117-46 2,933,415 4/1960 Homer et al.29--191 2,936,229 5/1960 Shepard 750.55 2,949,358 8/1960 Alexander etal. 75--176 3,006,782 10/1961 Wheildon 29195 3,023,490 3/1962 Dawson29-195 DAVID L. RECK, Primary Examiner.

WILLIAM D. MARTIN, HYLAND BIZOT, Examiners.

V. E. SULLIVAN, R. O. DEAN, Assistant Examiners.

1. A FLAME SPRAY POWDER IN THE FORM OF INDIVIDUAL, SYNERGISTICALLY CLADPARTICLES OF A SIZE BETWEEN ABOUT 60 MESH AND PLUS 3 MICRONS COMPRISINGA NUCLEUS AND AT LEAST ONE COATING LAYER OF A MATERIAL DIFFEREING FROMSAID NUCLEUS, ONE OF SAID COATING LAYER AND NUCLEUS COMPRISING AREFRACTORY SELECTED FROM THE GROUP CONSISTING OF REFRACTORY OXIDES,REFRACTORY CARBIDES, AND DIAMOND THE OTHER A BONDING MATRIX FOR SAIDREFRACTORY MATERIAL SELECTED FROM THE GROUP CONSISTING OF NICKEL ANDCOBALT MATRICES.